Ok so a lot of people bring this up as a big plothole that Bill and Fleur could be their own secret keeper, and why didn't the Potters just do the same, etc.. etc...

Well i think i have an explanation for this that can semi makes sense:

So Bill and Fleur make themselves the secret keeper for the shell cottage in 1997, and the Potters make Peter the secret keeper around 1980.

That's a 17 year difference.

Now, we all know that spells can be created, as evidenced by Snape creating his own spells during Hogwarts. How easy it is to do, we don't know, (though if a teenager can do it, it surely can't be that hard?) but i think by that logic it would make sense that existing spells can also be improved/expanded if someone is powerful enough and knows how to do it.

So, what if that by 1997, the Fidelius have been expanded to be able to include yourself as a secret keeper, thus eliminating the need for a third party? I think this would make perfect sense.

Just think of it this way:

The Potters are famously betrayed and killed, it's all in the news, etc... This causes a shock throughout the wizarding world, and many suddenly start to feel unsafe. It was unthinkable before that the secret keeper would decide to betray their secret, and nobody even really thought about a scenario like this. For this reason, maybe a group, the ministry, or someone powerful enough decides to experiment with the Fidelius, and over the next 17 years, expands it so that now, you can be your own secret keeper. Bill also works as a curse breaker for Gringotts, so it makes even more sense that he'd be someone powerful enough to do this and or have the knowledge thanks to his experience with ancient artifacts and the backing of the goblins.

What do you guys think?